Oxygen-enriched air feed for a non-ferrous metal production unit

ABSTRACT

All of the air is compressed in a single compressor ( 1 ), which feeds the smelter ( 2 ) for smelting the ore, the converter ( 6 ) for converting the matte coming from the smelter ( 2 ) and an air separation unit ( 4 ) which delivers two oxygen streams ( 9, 10 ) for enriching the air. A buffer tank ( 7 ) is used to deliver a variable flow of enriched air to the converter ( 6 ). Application to the production of copper.

[0001] The present invention relates to a process for feedingoxygen-enriched air into a non-ferrous metal production unit comprising,on the one hand, a smelter for smelting an ore concentrate of the saidmetal, fed by continuously injecting oxygen-enriched air and, on theother hand, a converter for converting the matte coming from thesmelter, fed by injecting oxygen-enriched air with a variable flow rate,and to a plant for implementing this process. The invention applies inparticular to the production of copper.

[0002] The pressures mentioned below are absolute pressures.

[0003] Copper production units conventionally consist of a smelteroperating continuously, such as a flash furnace, a Noranda furnace or aTeniente furnace, and of a converter operating batchwise, such as aPierce converter or a Hoboken converter.

[0004] The raw material, composed of copper ore concentrate, is chargedinto the smelter, in which it becomes enriched with copper. Acopper-rich mixture called “matte”, containing by weight approximately60 to 70% copper, is then obtained. This matte is then further enrichedwith copper in the converter and is converted into what is called“blister” copper containing approximately 99% copper.

[0005] In order for the smelting and the conversion to take placecorrectly, the smelter and the converter are fed with streams ofoxygen-enriched air. The smelter consumes a constant stream ofoxygen-enriched air. In contrast, the converter consumes a variablestream of oxygen-enriched air. Moreover, this stream may be close tozero when, the conversion into blister copper having been completed, theladle of the converter is emptied in order to recover the blister copperand thus be able to start a new copper production cycle. Typically, acopper production cycle lasts approximately two hours, distributed asfollows:

[0006] oxygen-enriched air is injected into the converter forapproximately one hour;

[0007] the injection is stopped, the slag floating on the surface of theliquid copper is removed, the ladle is drained in order to recover thecopper, after which the ladle is recharged with matte and a new cycle isstarted.

[0008] While the ladle is being drained, a gentle stream ofoxygen-enriched air is maintained in order to maintain the flame of theconverter burners. The degree of oxygen enrichment of the air depends onthe composition of the raw material and on the expected production. As ageneral rule, the stream of air feeding the smelter is enriched with upto 28% oxygen and the stream of air feeding the converter is enrichedwith 50 to 60% oxygen.

[0009] Conventionally, the smelter and converter each have an airblower, the stream of air from which is enriched by injecting oxygenproduced by a plant independent of the two air blowers.

[0010] Since the consumption of oxygen-enriched air by the smelter isconstant, the air blower connected to the smelter permanently producesan air stream corresponding to the maximum flow rate of the copperproduction cycle. In contrast, since the consumption of oxygen-enrichedair by the converter is variable, the difference between the output ofair produced by the blower connected to the converter, which operatescontinuously, and that consumed by this converter is generally vented toatmosphere.

[0011] The oxygen production plant consists of an air compressor and anair separation unit which is capable of delivering a variable flow ofoxygen so as to enrich the air stream of the blower for the smelter witha constant oxygen stream and to enrich the air stream for the converterwith a variable oxygen stream.

[0012] The term “compressor” is understood here to mean an actualcompressor or several compressors mounted in parallel and having acommon delivery.

[0013] This process for producing oxygen-enriched air by a plantcomprising two independent air blowers connected to an oxygen productionunit has various drawbacks, such as large overall size, considerableenergy consumption and not insignificant loss of energy due to the airdelivered by one of the blower being vented to atmosphere.

[0014] It is therefore an object of the invention to provide a processand a plant for feeding oxygen-enriched air into a non-ferrous metalproduction unit, which is smaller in overall size and which allows theenergy expenditure to be substantially reduced.

[0015] The subject of the invention is therefore a process for feedingoxygen-enriched air into a non-ferrous metal production unit comprising,on the one hand, a smelter for smelting the concentrate of the saidmetal, fed by continuously injecting oxygen-enriched air and, on theother hand, a converter for converting the matte coming from thesmelter, fed by injecting oxygen-enriched air with a variable flow rate,characterized in that:

[0016] all of the air is compressed in a single compressor capable offeeding the smelter and the converter;

[0017] some of this compressed air is treated in an air separation unitin order to obtain two oxygen streams which are injected into thecompressed air intended for feeding the smelter and the converter,respectively; and

[0018] the compressed air or oxygen-enriched compressed air intended forthe converter is stored in a buffer tank when the consumption ofoxygen-enriched air by the converter is below a predetermined thresholdand compressed air or oxygen-enriched compressed air is removed from thebuffer tank when the consumption of oxygen-enriched air by the converteris above the said threshold.

[0019] According to other features of this process:

[0020] the smelter is fed by mixing air compressed by the firstcompression level of the compressor with oxygen produced by the airseparation unit substantially at the same pressure;

[0021] the air separation unit is fed with compressed air by acompression level of the compressor located behind the first compressionlevel of this compressor;

[0022] the converter is fed by mixing air compressed by the compressorto a pressure above the feed pressure of this converter with oxygenproduced by the air separation unit substantially at the same pressure,by storing the oxygen-enriched air in the said buffer tank when theconsumption of oxygen-enriched air by the converter is below the saidthreshold and by removing oxygen-enriched air from this buffer tankthrough an expansion device when the consumption of oxygen-enriched airby the converter is above the said threshold;

[0023] air compressed by the final stage of the compressor to a pressureabove the feed pressure of the converter is stored in the said buffertank when the consumption of oxygen-enriched air by this converter isbelow the said threshold and the converter is fed by mixing air storedin the buffer tank and/or air compressed by the final stage of thecompressor, both air streams being removed through an expansion device,with oxygen produced by the air separation unit at a variable rate andat a pressure substantially equal to the feed pressure of the converter;

[0024] the air intended for the converter is compressed by the finalstage of the compressor.

[0025] The subject of the invention is also a plant for implementing theprocess defined above. This plant is characterized in that it comprises:

[0026] an air separation unit designed to deliver oxygen to the smelterand the converter;

[0027] a single air compressor, the delivery side of which is connectedto the smelter, to the air separation unit and to the converter viafirst, second and third lines respectively; and

[0028] a buffer tank connected to the said third line.

[0029] According to other features of this plant:

[0030] the buffer tank is also connected, on the one hand, to an oxygenoutput line from the separation unit intended for the converter and, onthe other hand, to this converter via an expansion device. The buffertank is also connected to the converter via an expansion device and anoxygen output line from the separation unit intended for the converterruns into the line which connects this expansion device to theconverter.

[0031] the air separation unit comprises two oxygen production circuits,one feeding the smelter and the other feeding the converter;

[0032] the oxygen production circuit feeding the converter is providedwith means for adjusting the oxygen flow rate;

[0033] the air separation unit is a double-column air distillation unitwhich includes a swing system so as to produce a variable stream ofoxygen by distillation of a constant air input;

[0034] the air compressor comprises at least two compression levels, thedelivery of the first level being connected to the said first line andthe delivery of the following level or levels being connected to thesaid second and third lines;

[0035] the compressor has three compression levels, the deliveries ofwhich are connected to the said first, second and third lines,respectively.

[0036] As will have been understood, the invention essentially consistsin combining the air production with the oxygen production so thatoxygen-enriched air for feeding the smelter and the converter of anon-ferrous metal production unit is produced more economically.

[0037] Illustrative examples of the invention will now be described withreference to the appended drawings in which:

[0038]FIG. 1 shows schematically a plant for producing oxygen-enrichedair feeding a copper smelter and a copper converter; and

[0039]FIG. 2 shows an alternative embodiment of the plant in FIG. 1; and

[0040]FIG. 3 shows an air separation unit intended for the plant of FIG.2.

[0041]FIG. 1 shows a copper production plant which comprises a singleair compressor 1 having 3 compression levels (i.e. for example 4 or 5stages) feeding compressed air respectively into, firstly, a smelter 2via a first line 3, secondly an air separation unit 4 via a second line5 and, finally, a converter 6 or a buffer tank 7 via a third line 8. Theair separation unit 4 producing the oxygen has two separate outputcircuits delivering oxygen at different pressures, one 9 feeding thesmelter 2, the other 10 feeding the converter 6. Each circuit 9, 10 is acircuit with a constant flow rate.

[0042] The buffer tank 7 is capable of storing the compressed air andthe oxygen of the second circuit 10 when the consumption ofoxygen-enriched air by the converter 6 is low, that is to say below apredetermined threshold. An expansion valve 11, consisting of adownstream pressure regulator, is placed in a line 12 which connects theconverter to the buffer tank 7, in order for the stream ofoxygen-enriched air to flow in the circuit 12 and to be injected intothe converter 6 when the consumption by this unit 6 is high, that is tosay above the said threshold.

[0043] The plant in FIG. 2 differs from the previous one by the factthat the air separation unit 4 here is equipped with a system called a“swing” system, described later, allowing a variable flow of oxygen tobe delivered to the converter 6 while the unit 4 handles a constant flowof air. In addition, the expansion valve 11 is placed between the tank 7and the point 13 where the oxygen produced by the circuit 10 meets theline 12 for feeding enriched air into the converter 6.

[0044] In operation, in the case of FIG. 1, all of the air needed tooperate the copper production unit is compressed in the compressor 1.

[0045] Some of this air, extracted from the delivery of the firstcompression level of the compressor 1, at a constant pressure of between1.2 and 1.7 bar, is injected at a constant flow rate into the smelter 2after having been enriched by an oxygen stream 9, at a pressuresubstantially equal to that of the air stream produced at a constantflow rate by the air separation unit 4.

[0046] Some of the air coming from one of the following compressionlevels (for example, the second compression level) of the compressor 1passes through the air separation unit 4. The latter delivers, on theone hand, an oxygen stream 9 at a pressure of 1.2 to 1.7 bar feeding thesmelter 2, and, on the other hand, a second oxygen stream 10 at apressure of 5 to 10 bar intended for the converter 6. The remainder 8 ofthe compressed air is extracted from the final stage of the compressor 1at a pressure of approximately 5 to 10 bar and is joined to theaforementioned oxygen stream 10. The enriched air thus obtained feedseither the buffer tank 7, when the consumption of oxygen-enriched air islow, or the converter 6 via the expansion valve 11, when the consumptionof enriched air is high.

[0047] According to the variant in FIG. 2, the air separation unit 4delivers a first oxygen stream 9, at a constant flow rate and at apressure of 1.2 to 1.7 bar, which feeds the smelter 2. The airseparation unit also delivers a second oxygen stream 10 at a pressure ofapproximately 1.5 bar, which feeds the converter 6, a swing beingprovided so as to deliver the oxygen at a variable flow rate dependingon the consumption of enriched air by the converter 6.

[0048] The remainder 8 of the compressed air is extracted from the finalstage of the compressor at a pressure of approximately 5 to 10 bar. Whenthe consumption of oxygen-enriched air by the converter 6 is low, thisair is partly stored in the buffer tank 7. At any instant, a flow of airequal to the difference between the flow of enriched air demanded by theconverter 6 and the flow of oxygen 10 passes through the expansionvalve.

[0049] To meet the abovementioned saving criteria the air produced bythe air compressor and feeding the air separation unit and the tank 7 isat a pressure corresponding to an optimum value from the economic andenergy standpoints between the energy expended for compressing the airand the cost corresponding to the investment in the buffer tank allowingthe converter to be fed with enriched air in a discontinuous manner.

[0050] Thus, the pressure of the air produced by the air compressor forfeeding the air separation unit is preferably from 5 to 6 bar and thepressure of the air produced by the air compressor for feeding the gastank is preferably from 5 to 10 bar.

[0051] The air separation unit 4 shown in FIG. 3, of the conventional“swing” type, is intended to deliver a variable flow of oxygen to theline 10 in FIG. 2. It basically comprises the air compressor 1 withthree compression levels, an apparatus 14 for drying and decarbonizingthe air by adsorption, a main heat exchange line 15, an air supercharger16, an auxiliary heat exchanger 17, a turbocompressor set comprising aturbine 18 coupled to a compressor 19, a variable-flow liquid oxygenpump 20, a liquid oxygen buffer tank 21, a liquid air buffer 22, adouble air distillation column 23, a subcooler 24 and a liquid nitrogenpump 25. The double column 23 is of the minaret type and comprises amedium-pressure column 26 surmounted by a low-pressure column 27, thelatter being extended upward by a short distillation section or minaret28 of smaller diameter. A main reboiler-condenser 29 brings the overheadvapour (almost pure nitrogen) of the column 26 into indirect heatexchange relationships with the liquid (liquid oxygen) in the bottom ofthe column 27.

[0052] In operation, a constant air flow coming from the secondcompression level of the compressor 1, brought back to near ambienttemperature at 30, purified at 14 and then cooled down to near its dewpoint at 15, is injected into the bottom of the column 26.

[0053] According to the conventional double-column distillation process,the double column 23 produces, with constant flow rates, liquid oxygen31 from the bottom of the column 27, low-pressure gaseous nitrogen 32from the top of the minaret 28 and medium-pressure liquid oxygen 33 fromthe top of the medium-pressure column 26.

[0054] The liquid oxygen withdrawn from the low-pressure column isstored in the buffer tank 21 and, consequently, is compressed to thepressure of the circuit 10 by the pump 20 and then vapourized whenflowing as a countercurrent through a stream of air with a constant flowrate supercharged at 16. The air thus liquefied is, after expansion tothe medium pressure in an expansion valve 34, stored in the buffer tank22 before being partially introduced in the liquid state into the lowerpart of the column 26 and, for the remainder, expanded to the lowpressure in an expansion valve 35 and introduced at an intermediatelevel of the column 27.

[0055] Conventionally, when the flow of gaseous oxygen needed in thecircuit 10 is less than 21% of the flow of distilled air, the pump 20 isslowed down correspondingly, and the liquid oxygen level rises in thetank 21. At the same time, since a lesser flow of air is liquefied, theliquid air level falls in the tank 22. The phenomena reverse should theoxygen flow in 10 increase to above 21% of the flow of distilled air.

[0056] Moreover, the unit 4 produces a constant flow of gaseous oxygenfor the circuit 9, for example from another line 36 for withdrawingliquid oxygen from the column 27, then vapourization/warming in 15 andpossibly compression of the resulting gaseous oxygen.

[0057] The unit 4 also produces a stream of low-pressure gaseousnitrogen coming from the minaret 28 and warmed in 24 and then in 15,together with a stream of high-pressure gaseous nitrogen obtained bymedium-pressure liquid nitrogen pumping in 25 followed byvapourization/warming in 15. These two nitrogen streams are used forinerting and/or conveying in the copper production plant.

[0058] The turbocompressor set 18,19, which operates by superchargingand expanding a portion of the incoming air, serves to keep the unit 4cold.

[0059] An air separation unit like that in FIG. 3 makes it possible toobtain a rate of variation of the oxygen output produced in 10 which istypically of the order of 5% per minute.

[0060] The invention may also be applied to the production ofnon-ferrous metals other than copper, such as nickel.

1. Process for feeding oxygen-enriched air into a non-ferrous metalproduction unit comprising, on the one hand, a smelter (2) for smeltingthe ore concentrate of the said metal, fed by continuously injectingoxygen-enriched air and, on the other hand, a converter (6) forconverting the matte coming from the smelter, fed by injectingoxygen-enriched air with a variable flow rate, characterized in that:all of the air is compressed in a single compressor (1) capable offeeding the smelter (2) and the converter (6); some of this compressedair is treated in an air separation unit (4) in order to obtain twooxygen streams (9, 10) which are injected into the compressed airintended for feeding the smelter (2) and the converter (6),respectively; and the compressed air or oxygen-enriched compressed airintended for the converter (6) is stored in a buffer tank (7) when theconsumption of oxygen-enriched air by the converter is below apredetermined threshold and compressed air or oxygen-enriched compressedair is removed from the buffer tank (7) when the consumption ofoxygen-enriched air by the converter (6) is above the said threshold. 2.Process according to claim 1, characterized in that the smelter (2) isfed by mixing air compressed by the first compression level of thecompressor (1) with oxygen produced by the air separation unit (4)substantially at the same pressure.
 3. Process according to claim 1 or2, characterized in that the air separation unit (4) is fed withcompressed air by a compression level of the compressor (1) locatedbehind the first compression level of this compressor.
 4. Processaccording to one of claims 1 to 3, characterized in that the converter(6) is fed by mixing air compressed by the compressor (1) to a pressureabove the feed pressure of this converter (6) with oxygen produced bythe air separation unit (4) substantially at the same pressure, bystoring the oxygen-enriched air in the said buffer tank (7) when theconsumption of oxygen-enriched air by the converter (6) is below thesaid threshold and by removing oxygen-enriched air from this buffer tank(7) through an expansion device (11) when the consumption ofoxygen-enriched air by the converter (6) is above the said threshold. 5.Process according to any one of claims 1 to 3, characterized in that aircompressed by the final stage of the compressor (1) to a pressure abovethe feed pressure of the converter (6) is stored in the said buffer tank(7) when the consumption of oxygen-enriched air by this converter (5) isbelow the said threshold and the converter is fed by mixing air storedin the buffer tank (7) and/or air compressed by the final stage of thecompressor (1), both air streams being removed through an expansiondevice (11), with oxygen produced by the air separation unit (4) at avariable flow rate and at a pressure substantially equal to the feedpressure of the converter (6).
 6. Process according to any one of claims1 to 5, characterized in that the air intended for the converter (6) iscompressed by the final stage of the compressor (1).
 7. Feed plant forimplementing a process according to any one of the preceding claims,characterized in that it comprises: an air separation unit (4) designedto deliver oxygen to the smelter (2) and the converter (6); a single aircompressor (1), the delivery side of which is connected to the smelter(2), to the air separation unit (4) and to the converter (6) via first,second and third lines; and a buffer tank (7) connected to the saidthird line.
 8. Feed plant according to claim 7, characterized in thatthe buffer tank (7) is also connected, on the one hand, to an oxygenoutput line from the separation unit (4) intended for the converter (6)and, on the other hand, to this converter (6) via an expansion device(11).
 9. Feed plant according to claim 7 or 8, characterized in that thebuffer tank (7) is also connected to the converter (6) via an expansiondevice (11) and in that an oxygen output line from the separation unit(4) intended for the converter (6) runs into the line which connectsthis expansion device to the converter (6).
 10. Feed plant according toany one of claims 7 to 9, characterized in that the air separation unit(4) comprises two oxygen production circuits, one (9) feeding thesmelter (2) and the other (10) feeding the converter (6).
 11. Feed plantaccording to claims 9 and 10 taken together, characterized in that theoxygen production circuit feeding the converter (6) is provided withmeans (20) for adjusting the oxygen flow rate.
 12. Feed plant accordingto claim 11, characterized in that the air separation unit (4) is adouble-column air distillation unit which includes a swing system (16,20 to 22) so as to produce a variable stream of oxygen by distillationof a constant air input.
 13. Feed plant according to any one of claims 7to 12, characterized in that the air compressor (1) comprises at leasttwo compression levels, the delivery of the first level being connectedto the said first line and the delivery of the following level or levelsbeing connected to the said second and third lines.
 14. Feed plantaccording to claim 13, characterized in that the compressor (1) hasthree compression levels, the deliveries of which are connected to thesaid first, second and third lines, respectively.